Solventless and high solids silicone pressure sensitive adhesives provide excellent cure, peel and tack adhesion properties on polyester, polyimide, and polytetrafluoroethylene tapes. However, some cured PSA tapes have a high affinity to the back side of adhesive tapes. This affinity is undesirable since it leads to difficulties in unwinding and slitting operations and inconsistency in tape appearance upon dispensing. This phenomenon is most apparent with adhesives having a polyester backing.
Some specific compositions which are curable to produce pressure sensitive adhesives, display this high affinity to the backside of adhesive tapes. In particular, these compositions include recently developed solventless or low solvent-containing organopolysiloxane compositions which comprise by weight: (A) from about 50 to about 75 parts by weight of a toluene and benzene soluble, resinous copolymer comprising R.sub.3 SiO.sub.1/2 units and SiO.sub.4/2 units wherein R is a monovalent hydrocarbon radical having from 1 to 6 carbon atoms; (B) an alkenyl-terminated polydiorganosiloxane; (C) an organohydrogenpolysiloxane compatible with the mixture of (A) and (B); (D) a catalytic amount of a hydrosilation catalyst; and (E) from 0 to about 40% by weight of an organic solvent.
Other specific compositions having such high backside affinities include compositions of the type described above which further comprise a hydrogen-containing polydiorganosiloxane containing more than two silicon-bonded hydrogen atoms per chain and being present in an amount such that (D) has a silicon-bonded hydrogen content of from about 10 to about 100 mole % based on the total silicon-bonded hydrogen content of (C) and (D).
When dispensing tapes having compositions of these types, the dispensing angle affects the surface smoothness and optical quality of the removed tapes. When dispensing a polyester-backed silicone adhesive at 180.degree. angle, a substantially clear, smooth undistorted adhesive tape can be obtained. However, at 90.degree., a more common dispensing angle, a relatively hazy, roughened tape is obtained. To adhesive tape manufacturers and users, it is desirable to have silicone pressure sensitive adhesives which can be dispensed with little caution using available equipment and settings and still obtain a smooth surface and minimal distorted optical characteristics.
Therefore, it is desirable to develop methods and compositions curable to form silicone adhesives with improved resistance to distortion and haze upon removal from a finished tape roll, regardless of the dispensing angle.